Sometimes, in a communication system that is structured from a plurality of communication devices such as computers and routers (hereinafter termed “nodes”) that are connected to a network, there is the need for operations to run properly continuously, depending on the application and purpose. For example, in communication systems that perform control and management of manufacturing lines to achieve improved manufacturing efficiency in product manufacturing, or communication systems for monitoring operations and controlling maintenance of equipment that operates continuously on a large scale, such as in plant equipment, or the like, there is the need for communication systems that operate continuously with stability.
Conventionally, in these types of communication systems, construction of redundant structures through the provision of a plurality of nodes having identical functions, so that if one node were to fall into a non-operating state, the other nodes, having identical functions, would continue to operate, has been used as means for achieving stable and continuous system operations.
Japanese Unexamined Patent Application Publication 2009-32120 (“JP '120”) discloses, as a technology for achieving a redundant structure in a communication system such as set forth above, a technology wherein a plurality of server devices, having identical functions, is provided in a communication system wherein server devices and client devices perform data communication through a network, wherein, if one server device were to become inoperable, the communication destination of the client device that has requested processing from a server device switches to another server device having identical functions.
However, the technology disclosed in JP '120 is one wherein a function for monitoring the state of operations of a server device is provided in a client device, or wherein a function for controlling the state of operation of the communication network as a whole is provided in the communication network in order to switch the server device with which the client device communicates. Consequently, in order to achieve stable and continuous operations of the communication system through a redundant structure for the server devices, both the server devices and the client devices will have structures that are complex and specialized, both in terms of hardware and in terms of software, and thus there is a problem in that the production thereof is extremely costly and time-consuming.
Furthermore, in recent years there have been increasing demands for stable and continuous operations in not just the large-kale, high-cost communication systems, but in small-scale and inexpensive communication systems as well.
The present invention is to solve the problems set forth above, and the object thereof is to provide a communication system that achieves stable and continuous operations, wherein the redundant structure can be constructed easily.